Personal care products typically are made with a top sheet material (also referred to as a cover sheet or liner), an absorbent core and a liquid impervious back sheet. Some may also have a surge layer or other specialized layers between the top sheet and absorbent core. Absorption of fluid, comfort and avoidance of leakage are the functions desired.
In the making of absorbent webs it is often desirable that a uniform distribution be accomplished across the web when placing the absorbents within the web structure. Such absorbents may include natural absorbents, including cellulosic material such as wood pulp, and superabsorbent materials, as are known in the art. If a uniform distribution is not achieved across the web, product absorbency may suffer, or material may be wasted in the making of the absorbent web.
In nonwoven airlaid materials, as known in the art, nonwoven web constituents are entrained into an air stream and deposited on a forming wire, or web, and subsequently fixed in place by various means, such as heating. However, uniform entrainment of the various constituent materials is often problematic. The thermoplastic fibers, thermoplastic binders, cellulosic or other absorbent fibers, and superabsorbent materials, may come in a variety of forms, such as substantially continuous fibers, staple fibers, liquids, and particulates. The constituent materials may further be in a variety of weights, sizes and morphologies, as will be known to those of skill in the art.
Various methods have been proposed to alleviate uneven deposition of constituent materials for the nonwoven web onto the forming wire. One such method, often called a Dan-Web process, is exemplified in U.S. Pat. No. 4,640,810, to Laursen et al., in which the constituent materials are air-entrained through two perforate screen chambers, or tubular forming screens, located inside a forming head. The forming screens have particle-distributing rotary members therein for dispersing the constituent materials through the screens into the forming head and onto the forming wire. U.S. Pat. No. 5,885,516, to Christensen et al., teaches a similar system of particle distribution but with superabsorbent powder being distributed by a separate chute located between the forming screens and substantially at the bottom thereof. It has been found that achieving the proper mix of air currents to obtain uniform distribution of the materials in such systems can be problematic. Particulate constituent materials such as the superabsorbents, may especially be caused to aggregate, leading to wasted materials, or unsatisfactory performance for use in personal care absorbent articles. Other problems may include long process equilibrium times resulting from particulate build-up in the forming pipes and excessive equipment wear due to the abrasive nature of certain particulates.
Bicomponent nonwoven filaments are known in the art generally as thermoplastic filaments which employ at least two different polymers combined together in a heterogeneous fashion. Instead of being homogeneously blended, two polymers may, for instance, be combined in a side-by-side configuration, so that a first side of a filament is composed of a first polymer xe2x80x9cAxe2x80x9d and a second side of the filament is composed of a second polymer xe2x80x9cB.xe2x80x9d Alternatively, the polymers may be combined in a sheath-core configuration, so that an outer sheath layer of a filament is composed of a first polymer xe2x80x9cA,xe2x80x9d and the inner core is composed of a second polymer xe2x80x9cB.xe2x80x9d Other heterogeneous configurations are also possible.
Pulp fibers have been employed in certain absorbent applications to enhance the absorbency. U.S. Pat. No. 4,530,353, issued to Lauritzen, discloses pulp fibers in combination with staple length bicomponent fibers used in the manufacture of absorbent bandages. In that case, the fibers also contain high and low melting polymers. The staple length fibers are bonded together by melting only the lower melting component. Likewise, superabsorbent materials, alone or in combination with pulp such as taught in published application WO 00/62922 (U.S. Ser. No. 09/546,634), fibers have been employed in certain absorbent applications to enhance the absorbency.
There is a need or desire for an absorbent nonwoven web composite which exhibits good softness and strength with a high degree of absorbency. There is a further need to achieve a high degree of absorbent particle loading in a nonwoven web to economically and efficiently make highly absorbent webs for personal care absorbent articles. This need exists for diapers, training pants, wipes, and other personal care absorbent articles where comfort, strength, and absorbent performance are all important.
There remains a need in the art for improved distribution of constituent materials in the making of absorbent nonwoven webs and alternative means and methods for achieving such distribution. It is further desirable that such means and methods achieve a high degree of absorbent material concentration within the web when required for particular product applications.
In response to the discussed difficulties and problems encountered in the prior art, new methods and apparatuses has been discovered which may provide both a high degree of absorbent materials by weight within the web and uniform distribution of materials within the web. Personal care products using the resultant webs are also contemplated to be within the scope of this invention.
One such personal care product has a liquid impermeable backsheet, a liquid permeable topsheet, and an absorbent composite web located between the topsheet and backsheet. The absorbent composite web, hereinafter sometimes referred to simply as the web, according to one embodiment of the present invention, is a coformed web having major surfaces in the X-Y plane and a depth in the Z direction that is suitable for use as a fluid retention layer in a disposable absorbent article.
The web may contain a layer or layers of airlaid composite material which may have both thermoplastic fibers and absorbent material. The thermoplastic fibers desirably serve as a binder to the absorbent material. The thermoplastic fibers may be single component or multi-component fibers of various composition and may be present in amount of greater than or equal to about two weight percent in a web of binder fibers and absorbent materials.
The absorbent materials may be natural materials such as natural fibers including cellulosic materials such as staple fibers of wood pulp, or superabsorbent materials, or a combination of the natural and superabsorbent materials, and may be present in amounts of less than or equal to about ninety eight weight percent in a web of binder fibers and absorbent materials. The web may be provided with other layers such as forming tissues, films, or the like as desired for the ultimate product application of the web.
A method of achieving a web according to the present invention may include: passing the thermoplastic fibers and cellulosic fibers entrained in an airstream through tubular forming screens contained inside a forming head, the tubular forming screens having rotating distribution members within the tubular forming screens; and adding particulate superabsorbent within the forming head outside of, and/or above, the tubular forming screens with an air velocity substantially neutral to that of the forming head in order to avoid substantially interrupting the air flow within the forming head which might lead to uneven distribution of the web components. In another aspect of the present invention the method may include passing the thermoplastic fibers entrained in an airstream through tubular forming screens contained inside a forming head, and adding combined particulate superabsorbent and cellulosic fibers, or pulp-coated superabsorbents, within the forming head outside of, and above, the tubular forming screens with an air velocity substantially neutral to that of the forming head in order to avoid substantially disrupting the air flow within the forming head.
Apparatus for achieving the web according to the present invention may include means for entraining thermoplastic fibers and cellulosic fibers in an airstream; a forming head containing rotating tubular forming screens therein, the rotating tubular forming screens having means for accepting the airstream of entrained thermoplastic fibers and cellulosic fibers, the rotating tubular forming screens having rotating distribution members therein; and means for adding particulate superabsorbent within the forming head outside of the rotating tubular forming screens at locations upstream and downstream in the MD of the rotating tubular forming screens to avoid interrupting the air flow within the forming head which might lead to uneven distribution of the web components. In another aspect of the present invention the apparatus may include means for passing the thermoplastic fibers entrained in an airstream through tubular forming screens contained inside a forming head, and means for adding combined particulate superabsorbent and cellulosic fibers within the forming head outside of, and/or above, the tubular forming screens to avoid disrupting the air flow within the forming head. Such location may include placement of a chute outlet tangential to an upper quadrant of the tubular forming screens as further detailed below.